Block Copolymer Solutions Research Articles

Hierarchical Porous Block Copolymer Separator Membranes for Ultrahigh Rate Li-Ion Batteries

High-performance energy storage systems with reliable and sustainable electrochemical properties are urgently needed to satisfy the continuously surging demand in consumer electronics, electric vehicles (EVs), and grid-scale energy storage systems (ESSs). Among the enormours energy storage systems reported to date, lithium-ion rechargeable batteries (LIBs) have still garnered a great deal of attention. The rational design and fabrication of major battery components such as anodes, cathodes, electrolytes, and separator membranes are imperative prerequisites for the development of advanced batteries. Most research activities on battery components have been devoted to the electrochemically active materials, with a especially focus on electrode materials and electrolytes. Representative results include those related to high-voltage spinel nickel manganese oxides, overlithiated layer oxides, silicon- or metal alloys, functional electrolyte additives, and solid-state electrolytes. Taking into consider the fact that electrochemical performance of the batteries is basically governed by electron/ion transport phenomena, particular attention should be paid to battery separators as well as electrodes/electrolytes, because (i) all ions particiapted in Faradaic reaction of batteries should pass through electrolyte-filled porous separator membranes and (ii) Internal short-circuit failure occurring between electrodes (which is considered as a primary cause to trigger cell fire or explosion) is basically prevented by separator membranes. Currently, commercially available separators in LIBs are manufactured using polyolefin materials. These polyolefin separators have some advantageous attributes that render them suitable for practical use in LIBs. However, their intrinsic limitations (speci fically, sluggish/nonuniform ionic flow and poor thermal stability) often raise concerns regarding ion transport and electrical isolation between the electrodes. A large number of approaches to overcome these drawbacks have been undertaken, which include ceramic-coated separators, nonwoven separators, and electrospun nano fiber separators. Unfortunately, little attention has been devoted to controlling the ion transport phenomena in a separator, despite its important role in activating the electrochemical performance of cells. Here, as a new strategy to address these challenging issues, we demonstrate new surface energy-tailored amphiphilic polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) membranes with hierarchical multiscale hyperporous structures and chemical functionality (Figure 1), as a revolutionary membrane to enable remarkable advances in cell performance far beyond those achievable with conventional separators. Among the various building blocks for use in porous membranes, BCPs have been extensively investigated because of their self-assembly-enabled nanodomains. Through spinodal decomposition, breath figures, solvent swelling, and nonsolvent-induced phase separation (NIPS), BCPs can produce precisely defined porous structures in versatile shapes. Owing to facile and effective control of membrane morphologies, NIPS process, which is also known as immersion precipitation, has attracted great attention as a promising way to fabricate large-scale membranes. In the NIPS method, final morphologies (e.g., dense or porous, symmetric or asymmetric) of the membranes can be adjusted by combining the involved mass transport phenomena with corresponding phase separation. For membrane-driven purification and separation processes, asymmetric porous structure is preferable because it endows the membranes with both permeability and selectivity. Asymmetric structures with a well-organized skin layer were explored using self-assembled BCP films. Time-controlled evaporation of volatile solvent produces a skin layer with vertically aligned cylindrical structure supported by a graded porous layer, when the BCP solution was immersed into a nonsolvent. Meanwhile, porous membranes with symmetric structures are suitable for allowing two-way ionic transport, which is essentially required for separation membranes of rechargeable power sources. The macropore size of NIPS-based BCP membranes is basically determined by polymer concentrations and solvent-nonsolvent exchange kinetics, while their nanopore size strongly depends on the compatibility between pore-forming block and nonsolvent. In particular, construction of well-defined nanoporous morphology is highly required for advanced BCP membranes. However, even though BCPs, good solvent and nonsolvent are appropriately chosen, conventional NIPS-based BCP membranes normally generate poorly-developed nanopores due to a limited compatibility between pore-forming block and nonsolvent. To date, the most common way to tune nanoporous structure is limited to variation of molecular weight of pore-forming blocks. Our strategy for tailoring high porous BCP separator membrane is based on the introduction of a surface-energy-modifying agent, which allows fine-tuning of nanoscale phase separation between the surface-modified BCPs and nonsolvent. The surface-energy-modifying agent can be easily introduced into a pore-forming block of BCPs via nucleophilic substitution reaction. Depending on the degree of substitution, the surface-energy-modifying agent contributes to tuning dual (macro-/nano-) phase separation of the BCPs, which eventually enables the fabrication of hierarchical multiscale porous block copolymer membranes. The novel block copolymer separator membrane exhibited superior rate capability and cycle performance, owing to its precisely tuned, highly developed porous structure far beyond those achievable with conventional separator membrane technologies. Figure 1

Multipod structures of lamellae‐forming diblock copolymers in three‐dimensional confinement spaces: Experimental observation and computer simulation

ABSTRACTThe three‐dimensional (3D) confinement effect on the microphase‐separated structure of a diblock copolymer was investigated both experimentally and computationally. Block copolymer nanoparticles were prepared by adding a poor solvent into a block copolymer solution and subsequently evaporating the good solvent. The 3D structures of the nanoparticles were quantitatively determined with transmission electron microtomography (TEMT). TEMT observations revealed that various complex structures, including tennis‐ball, mushroom‐like, and multipod structures, were formed in the 3D confinement. Detailed structural analysis, showed that one block of the diblock copolymer slightly prefers to segregate into the particle surface compared with the other block. The observed structures were further elaborated using cell dynamics computer simulation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1702–1709

Interaction between Albumin and Pluronic F127 Block Copolymer Revealed by Global and Local Physicochemical Profiling.

The interaction of human serum albumin (HSA) with amphiphilic block copolymer Pluronic F127 has been investigated by several physical methods. Interest in studying this system stems from a broad range of bioactivities involving both macromolecules. Serum albumins constitute a significant class of proteins in the circulatory system, acting as carriers for a wide spectrum of compounds or assemblies. Pluronic block copolymers have revealed their capacity to ferry a variety of biologically active compounds. Circular dichroism, rheological measurements, and differential scanning microcalorimetry (μDSC) were employed to get insight into the interaction betweeen the two macromolecules. The results reveal that Pluronic F127 induces conformational changes to albumin if it is organized in a micellar form, while albumin influences the self-assembly of Pluronic F127 into micelles or gels. F127 micelles, however, induce smaller conformational changes compared to ionic surfactants. The μDSC thermograms obtained for HSA and/or F127 show that HSA shifts the critical micellar temperature (cmt) to lower values, while concurrently the HSA denaturation behavior is influenced by F127, depending on its concentration. Rheological measurements on solutions of F127 17% have shown that a sol-to-gel transition occurs at higher temperatures in the presence of HSA and the resulting gel is weaker. The global profile on HSA/F127 systems was complemented by local information provided by EPR measurements. A series of X-band EPR experiments was performed with spin probes 4-(N,N'-dimethyl-N-hexadecyl)ammonium-2,2',6,6'-tetramethylpiperidine-1-oxyl iodide (CAT16) and 5-doxyl stearic acid (5-DSA). These spin probes bind to albumin sites and are sensitive to phase transformations in Pluronic block copolymer solutions. For a given F127 concentration, the spin probe binds only to HSA below cmt and migrates to the F127 micelles above cmt. The collective data suggest soft interactions between the macromolecules, with the emerging results projecting potential applications linked to reaching optimal conditions for certain drug formulations.

Poly(glyoxylates): a new class of depolymerizable materials with amplified response to stimuli and applications in drug delivery

Event Abstract Back to Event Poly(glyoxylates): a new class of depolymerizable materials with amplified response to stimuli and applications in drug delivery Bo Fan1 and Elizabeth Gillies1, 2 1 The University of Western Ontario, Department of Chemical and Biochemical Engineering, Canada 2 The University of Western Ontario, Department of Chemistry, Canada Introduction: In recent years, there has been significant interest in stimuli-responsive materials[1],[2]. While successful in the lab, a challenge in their application is that numerous stimuli-mediated events are required to impart changes in properties. Self-immolative polymers (SIPs) were developed to address this limitation[3],[4]. Upon cleavage of a single stimulus-responsive end-cap, an SIP undergoes complete end-to-end depolymerization. Several SIP backbones including polycarbamates[5],[6], and poly(o-phthalaldehyde)s[7] have been developed. However, their application has been hindered by: 1) expensive, multistep monomer syntheses; 2) depolymerization to toxic species such as quinone methides or o-phthalaldehyde[8]. Described here is poly(ethyl glyoxylate) (PEtG) as a linear SIP and its application in stimuli-responsive micelles for drug delivery. PEtG can be synthesized from the commercially available monomer ethyl glyoxylate (EtG). Depolymerization produces glyoxylic acid hydrate[9], a metabolic intermediate in the glyoxylic acid cycle which has been shown to be non-toxic (Fig. 1b)[10]. Methods: EtG was distilled twice over P2O5, dissolved in CH2Cl2, and then polymerized for 1 h at -20 °C in the presence of NEt3 (Fig. 2)[11]. To end-cap the polymer, 1 was added. The solution was allowed to reach ambient temperature over 24 h then heated at 40 °C for 16 h. The polymer 2 was precipitated in methanol. A similar strategy could be used to also prepare PEtG with end-caps responsive to stimuli such as H2O2 or thiols by varying the structure of end-cap 1. Block copolymer 3 was formed by coupling with an azide-terminated poly(ethylene oxide) (PEO, 2 kg/mol) in N,N-dimethylformamide (DMF) in the presence of CuSO4 and sodium ascorbate. Self-assembly was performed by the addition of a dimethylsulfoxide (DMSO) solution of block copolymer into water followed by the removal of DMSO by dialysis. Doxorubicin loading was accomplished using a dialysis procedure[12]. Micelle degradation was triggered by irradiation with UV light (wavelength: 300-350 nm, 23 mWcm-2), while controls were kept in the dark. Results and Discussion: Polymerization of EtG afforded polymer 2 with a number average molar mass (Mn) of 42 kg/mol and a dispersity (Đ) of 2.0 based on size exclusion chromatography (SEC) in tetrahydrofuran relative to polystyrene standards. End-cap 1 is cleavable with UV light and also has an alkyne for conjugation of another polymer. Coupling of PEO was confirmed by a combination of SEC and NMR spectroscopy. Self-assembly of the resulting amphiphilic copolymer 3 afforded micelles with diameters of ~50 nm as measured by dynamic light scattering and transmission electron microscopy (Fig. 3a). Irradiation with UV light for 10 min resulted in rapid depolymerization of the micelles as measured by NMR spectroscopy. In contrast a non-irradiated control was stable for 24 h. To demonstrate the application of these micelles for triggered anti-cancer drug delivery, they were loaded with doxorubicin (Dox). Irradiation resulted in release of 75% of Dox over 50 h, in comparison with a control that was not irradiated and released only 20% of the drug over this time (Fig. 3b). Conclusions: PEtG was synthesized and capped with a moiety imparting responsiveness to UV light and enabling conjugation of PEO to afford an amphiphilic SIP. The copolymer assembled into micelles and these micelles rapidly depolymerized in response to UV light. The anti-cancer drug Dox was loaded into the micelles and they afforded selected release of Dox upon irradiation. These results, combined with the depolymerization of PEtG to non-toxic glyoxylic acid suggest the promise of these materials for drug delivery applications. It is also possible to easily tune the responsiveness to different stimuli by changing the end-cap. We thank the Natural Sciences and Engineering Research Council of Canada as well as Western University for funding this work.

Terminal groups control self-assembly of amphiphilic block copolymers in solution.

The terminal groups of amphiphilic block copolymers are shown to control macromolecular self-assembly in aqueous solutions, in the micellar/lamellar region of the phase diagram. At the same concentration and using the same self-assembly conditions, dramatic differences are observed in polymer hydration and the resulting nano-/microstructure for two series of polymers with identical block chemistry and hydrophilic-lipophilic balance (HLB). This suggests a strong contribution from end groups to the hydration as the initial step of the self-assembly process, and could be conveniently used to guide the particle morphology and size. Additionally, for polymers with those head groups which drive vesicular structures, differences in membrane organization affect their physical properties, such as permeability.

Micropore extrusion-induced alignment transition from perpendicular to parallel of cylindrical domains in block copolymers.

The orientation transition from perpendicular to parallel alignment of PEO cylindrical domains of PEO-b-PMA(Az) films has been demonstrated by extruding the block copolymer (BCP) solutions through a micropore of a plastic gastight syringe. The parallelized orientation of PEO domains induced by this micropore extrusion can be recovered to perpendicular alignment via ultrasonication of the extruded BCP solutions and subsequent annealing. A plausible mechanism is proposed in this study. The BCP films can be used as templates to prepare nanowire arrays with controlled layers, which has enormous potential application in the field of integrated circuits.

カテコール基含有ランダム・ブロック共重合体の合成とその応用展開

This review shows synthesis and application of catechol-containing random and block copolymers. We successfully synthesized amphiphilic random copolymers containing catechol moieties as side chains by free radical copolymerization of dopamine methacrylic amide and hydrophobic monomers including styrene. The synthesized amphiphilic copolymers firmly adhered onto inorganic materials and change surface properties from hydrophilic to hydrophobic. The polymer-immobilized inorganic nanoparticles can be dispersed in hydrophobic organic solvents and form porous hierarchic films after casting under humid conditions followed by calcination. Block copolymers containing catechol moieties have also been synthesized reversible addition-fragmentation transfer（RAFT）polymerization of 3,4-dihydroxy styrene and styrene followed by deprotection of methoxy groups. Metal ions can be reduced by using the synthesized block copolymers as templates and reductants, metal nanoparticles consequently formed by simple addition of metal ions into solution or film of catechol-containing block copolymers.

Orientation Control in Thin Films of a High-χ Block Copolymer with a Surface Active Embedded Neutral Layer.

Directed self-assembly (DSA) of block copolymers (BCPs) is an attractive advanced patterning technology being considered for future integrated circuit manufacturing. By controlling interfacial interactions, self-assembled microdomains in thin films of polystyrene-block-poly(methyl methacrylate), PS-b-PMMA, can be oriented perpendicular to surfaces to form line/space or hole patterns. However, its relatively weak Flory interaction parameter, χ, limits its capability to pattern sub-10 nm features. Many BCPs with higher interaction parameters are capable of forming smaller features, but these "high-χ" BCPs typically have an imbalance in surface energy between the respective blocks that make it difficult to achieve the required perpendicular orientation. To address this challenge, we devised a polymeric surface active additive mixed into the BCP solution, referred to as an embedded neutral layer (ENL), which segregates to the top of the BCP film during casting and annealing and balances the surface tensions at the top of the thin film. The additive comprises a second BCP with a "neutral block" designed to provide matched surface tensions with the respective polymers of the main BCP and a "surface anchoring block" with very low surface energy that drives the material to the air interface during spin-casting and annealing. The surface anchoring block allows the film to be annealed above the glass transition temperature of the two materials without intermixing of the two components. DSA was also demonstrated with this embedded neutral top layer formulation on a chemical patterned template using a single step coat and simple thermal annealing. This ENL technology holds promise to enable the use of high-χ BCPs in advanced patterning applications.

Fabrication of TiO2/WO3 Composite Nanofibers by Electrospinning and Photocatalystic Performance of the Resultant Fabrics

By coupling the self-assembly of polystyrene-block-poly(ethylene oxide)-containing titanium-tetraisopropoxide and tungsten hexaphenoxide (the precursors of TiO2 and WO3, respectively) with electrospinning technique, the hierarchically porous TiO2/WO3 composite nanofibers with inner-bicontinuous and outer-shell structures have been synthesized. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to characterize the structure of the fibers. In these nanofibers, the TiO2 acts as the frames, and WO3 fills the gaps. The UV–vis spectroscopy suggests that the spectral response range has been successfully extended into the visible regime. Furthermore, the resulting fabrics show enhanced performance in the photocatalytic degradation of acetaldehyde relative to neat TiO2 and neat WO3. Our results indicate that electrospinning the blend solution of block copolymer and two kinds of precursor of inorganic material is an effective strategy to fabricate composite nanofibers that can improve the photocatalytic activity of TiO2, especially for visible light.

Morphology of crystalline-amorphous olefin block copolymers in solution characterized by small-angle neutron scattering and microscopy.

The single-chain properties and self-assembly behavior in dilute solution of olefin block copolymers obtained by chain-shuttling technology and consisting of alternating crystallizable and amorphous ethylene/1-octene blocks were investigated by pinhole and focusing small-angle neutron scattering techniques, optical microscopy in bright-field and crossed-polarizer modes, and differential scanning calorimetry. The complex hydrocarbon soluble (precipitant free) macro-aggregates formed with decreasing temperature are characterized by spherulitic textures. The spherulites yield, on one hand, a morphology that depends on the chain structure properties and, on the other hand, multiple structural levels with a hierarchical organization that ranges from 10 Å up to tens of micrometres. This morphology displays peculiarities dictated by the polydisperse character of these materials.

Synthesis and morphology of polyacrylate-poly(dimethyl siloxane) block copolymers for membrane application

Poly(methyl acrylate)-poly(dimethyl siloxane)-poly(methyl acrylate) (PMA-PDMS-PMA) and poly(methyl methacrylate)-poly(dimethyl siloxane)-poly(methyl methacrylate) (PMMA-PDMS-PMMA) triblock copolymers were synthesized with atom transfer radical polymerization technique. Thermodynamic properties of block copolymer solutions were investigated. Solubility parameter differences and Flory-Huggins interaction parameters of block copolymer-solvent systems were evaluated for the membrane application. Morphology study indicated cylindrical micelles of PDMS block copolymers. X-Ray analysis confirmed phase separated morphology of PDMS block copolymers in bulk. The effect of polyvinyl acetate (PVAc) on the morphology and its effect on the gas permeation behavior of PMA-PDMS-PMA triblock copolymer was studied. PMA-PDMS-PMA/PVAc blend membranes were shown a new fibrillar morphology. The gas permeation properties and selectivity of the blend membranes were also reported. Open image in new window

Hierarchical Polymer-Carbon Nanotube Hybrid Mesostructures by Crystallization-Driven Self-Assembly.

Multistep crystallization-driven self-assembly has great potential to enable the construction of sophisticated hybrid mesostructures. During the assembly procedure, each step modifies the properties of the overall structure. Here, we demonstrate the flexibility and efficiency of this approach by preparing polymer-carbon nanotube (CNT) hybrid mesostructures. We started by growing polyferrocenyldimethylsilane (PFS) homopolymer crystals onto multiwalled CNTs. This first step facilitated the redispersion of the coated CNTs in both polar (2-propanol) and nonpolar (decane) solvents. In the second step of hybrid construction, a unimer solution of a PFS block copolymer was added into the PFS-CNT solution. The PFS coating on the CNT initiated the growth of elongated micelles, resulting in structures that resembled hairy caterpillars. PFS-b-P2VP (P2VP = poly-2-vinylpyridine) micelles were grown from the surface of PFS-CNT hybrids in 2-propanol, and PFS-b-PI (PI = polyisoprene) micelles were grown from these hybrids in decane. These micelles, by transmission electron microscopy were seen to have an unusual wavy kinked structure, very different from the uniform smooth structures normally formed by both block copolymers. For hybrids with PFS-b-PI micelles, cross-linking of the micelle coronas locked the whole structure in place and allowed us to use the partial oxidation of PFS components to grow metal nanoparticles in the core of these micelles. We finally investigated the influence of the corona-forming block used to grow the micelles on the wettability of films made from these mesostructures. Films formed with CNT hybrids grafted with PFS-b-PI micelles were superhydrophobic (contact angle, 152°). In contrast, the surface of the films was much more hydrophilic (contact angle, 54°) when they were prepared from CNT hybrids grafted with PFS-b-P2VP micelles.

Block copolymer-mediated synthesis of silver nanoparticles from silver ions in aqueous media

Abstract We report here on the silver (Ag) nanoparticle synthesis in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide) (PEO–PPO) block copolymers in the absence of any additional agents. In particular, we examined the effect of reaction temperature, molecular weight of PEO–PPO block copolymer and PEO–PPO block copolymer concentration on the reduction of silver ions (Ag + ) and the resulting formation of Ag nanoparticles in aqueous PEO–PPO block copolymer solutions. We found that Ag nanoparticles were formed from aqueous silver nitrate (AgNO 3 ) solutions containing PEO–PPO block copolymer above 100 °C. This is most likely due to the dehydration of Ag + caused by thermal motion of water molecules in higher-temperature aqueous solution at high vapor pressure. We also found that the formation of Ag nanoparticles in aqueous PEO–PPO block copolymer solutions was enhanced with larger molecular weight of PEO–PPO block copolymer and with increase in the concentration of PEO–PPO block copolymer in aqueous solutions.

Intermolecular Interactions and Self-Assembly in Aqueous Solution of a Mixture of Anionic–Neutral and Cationic–Neutral Block Copolymers

We have investigated the self-assembly in dilute aqueous solutions of a mixture of an anionic–neutral block copolymer (AP) and a cationic–neutral block copolymer (MP) by changing the added sodium chloride (NaCl) concentration CS or electrostatic interactions among oppositely charged blocks, by direct observation, optical and electron microscopies, and small-angle X-ray scattering. The ratio of the charged to neutral block chain lengths was ca. 10, and the total copolymer concentration and the mixing ratio (the mole fraction of the MP charge unit in the total charge units) of AP and MP were fixed to be 0.005 g/cm3 and 0.6, respectively. With decreasing CS from 2 to 0 M, we have found reentrant one-phase, two-phase, one-phase transitions in the aqueous solution of the AP–MP mixture. The two-phase to one-phase transition at CS ∼ 0.5 M arises from the competition between the macroscopic phase transition and micellization, which is the first observation in dilute block copolymer solutions. Moreover, we have fo...

Multigeometry Nanoparticles: Hybrid Vesicle/Cylinder Nanoparticles Constructed with Block Copolymer Solution Assembly and Kinetic Control

We report an experimental study of the assembly of various multicompartment and multigeometry nanoparticles constructed from mixtures of two diblock copolymers. By simply blending the amphiphilic block copolymers poly(acrylic acid)-block-polyisoprene (PAA-b-PI) and poly(acrylic acid)-block-polystyrene (PAA-b-PS), we constructed complex nanostructures including multigeometry vesicle–cylinder particles, multicompartment vesicles, or multigeometry cylinder–disk nanoparticles via kinetic control of solution assembly. In our assembly strategy, the PAA common domain in both block copolymers was first complexed with organic diamine molecules in organic solution to form a particle core. Therefore, the two different hydrophobic blocks from the two different polymers were trapped into the same particle. After addition of water, the particles form the structure having hydrophobic cores and PAA-amine hydrophilic shells; the two hydrophobic domains locally nanophase-separated in the core to form the multicompartment a...

In Situ Nanolithography with Sub-10 nm Resolution Realized by Thermally Assisted Spin-Casting of a Self-Assembling Polymer.

In situ nanolithography is realized based on warm spin-casting of block copolymer solutions. This advancement is based on Si-containing block copolymers with an appropriate thermodynamic driving force for spontaneous phase-separation combined with the thermal assistance provided by slight temperature elevations during the spin-casting. Sub-10 nm half-pitch nanoscale patterns are produced within 30 s without a separate annealing process.

Self‐Assembly‐Driven Electrospinning: The Transition from Fibers to Intact Beaded Morphologies

Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photonics due to their particular shape and surface morphology. Electrospinning, typically used for producing nanofibers, can also be used to fabricate polymer beads if the solution has a sufficiently low concentration. In this work, a novel approach for producing more uniform, intact beads is presented by electrospinning self-assembled block copolymer (BCP) solutions. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Herein, to demonstrate the technology, a well-studied polystyrene-poly(ethylene butylene)-polystyrene triblock copolymer is dissolved in a co-solvent system. The effect of solvent composition on the characteristics of the fibers and beads is intensively studied, and the mechanism of this fiber-to-bead is found to be dependent on microphase separation of the BCP.

Micellization of polyoxyethylene–polyoxypropylene block copolymers in aqueous polyol solutions

The micellization of a representative polyoxyethylene–polyoxypropylene–polyoxyethylene (POE–POP–POE) amphiphilic block copolymer (Pluronic P105, EO37PO58EO37) in aqueous solutions of the common excipients glucose, glycerol or ethanol, has been investigated as a function of solute (solvent) concentration, block copolymer concentration, and temperature. The formation of POE–POP–POE micelles is favored in the presence of glucose or glycerol, while ethanol has the opposite effect. ΔH° and ΔS° values derived from analysis of critical micellization concentration (CMC) data are both positive in all mixed aqueous polyol systems. ΔH° and ΔS° decrease slightly with increasing glucose or glycerol content, but increase significantly in the presence of ethanol. A 10- to 100-fold increase of the amphiphilic block copolymer solution viscosity was observed in the presence of glucose or glycerol above a certain temperature. This viscosity increase is indicative of micelle shape changes from spherical to elongated. The CMC and viscosity changes caused by glucose and glycerol are attributed to the enhanced dehydration of the POE block of the polymeric amphiphile. Glucose is more effective than glycerol, apparently due to its higher hydration number.

Synthesis, self-assembly and photo-responsive behavior of AB2 shaped amphiphilic azo block copolymer

Abstract In this work, we report the synthesis of AB 2 shaped amphiphilic azo block copolymer by macromolecular azo coupling reaction. The product and intermediates were characterized by various methods. The self-assembly in selected solvents and photo-responsive behavior of the copolymer were studied by means of UV–vis spectrophotometry and TEM. Spherical aggregates can be obtained by gradually adding water into the solution of this amphiphilic azo block copolymer. Upon irradiation with polarized UV (365 nm) light, the aggregates can be elongated in the polarized direction.

Filtration-based synthesis of micelle-derived composite membranes for high-flux ultrafiltration.

Ideal membrane configurations for efficient separation at high flux rates consist of thin size-selective layers connected to macroporous supports for mechanical stabilization. We show that micelle-derived (MD) composite membranes combine efficient separation of similarly sized proteins and water flux 5-10 times higher than that of commercial membranes with similar retentions. MD composite membranes were obtained by filtration of solutions of amphiphilic block copolymer (BCP) micelles through commercially available macroporous supports covered by sacrificial nanostrand fabrics followed by annealing and removal of the nanostrand fabrics. Swelling-induced pore generation in the BCP films thus covering the macroporous supports yielded ∼210 nm thin nanoporous size-selective BCP layers with porosities in the 40% range tightly connected to the macroporous supports. Permselectivity and flux rates of the size-selective BCP layers were adjusted by the BCP mass deposited per membrane area and by proper selection of swelling times. The preparation methodology described here may pave the way for a modular assembly system allowing the design of tailored separation membranes.